As known, the use of disc brakes is now common in bicycles. Such brakes are, indeed, often preferred to conventional brakes of different design since they ensure a high braking force and are less subject to problems caused by mud or water.
Typically, a disc brake is part of a hydraulic braking system that comprises a caliper fixed onto the frame of the bicycle, a brake disc mounted on the hub of the wheel and a brake lever positioned on the handlebars.
Inside the caliper there are two or four pistons active on two opposite brake pads. The brake disc rotates inside the space defined between the opposite pads.
The brake lever is connected to the brake caliper by a flexible tube. The brake lever is equipped with a fixed portion firmly fastened to the handlebars and a mobile portion, usually a lever hinged to the fixed portion and actuatable by the cyclist.
Inside the fixed portion of the brake lever there is usually a main cylinder in which a piston moves for placing the hydraulic circuit under pressure when the cyclist actuates the mobile portion of the brake lever. The main cylinder thus actuates the pistons of the brake caliper that bring the pads towards one another, generating friction on the brake disc and, consequently, braking the wheel.
The brake liquid that flows inside the hydraulic braking system is incompressible, so as to immediately transmit hydraulic forces from the brake lever to the brake caliper.
Therefore, it is necessary to ensure that there is no air inside the braking system since, as it is highly compressible, it would compromise the correct operation of the system.
For this purpose, it is known to equip the hydraulic braking system with a bleeding valve that allows the air present in the system to be expelled. Such a bleeding valve is often also used to introduce brake liquid into the hydraulic system.
Usually, the bleeding valve is arranged on the brake caliper and comprises an internally hollow valve body inserted in a hole made in the brake caliper. The hole in the brake caliper is in fluid communication with the hydraulic circuit. By rotating the valve body inside the hole in the brake caliper, the inner cavity of the valve body is placed in fluid communication with the hydraulic circuit to allow the air expulsion and/or brake liquid insertion operations.
The inner cavity of the valve body has a lip on top that projects from the brake caliper and that is closed by a sealing element to prevent dust, mud or dirt to enter into the cavity of the valve body during normal use of the bicycle.
Such a lip allows a tube of flexible material to be coupled with the bleeding valve, so that the air can come out from such a tube or so that the brake liquid can be inserted into the system through it.
As stated, the bleeding valve is usually arranged on the brake caliper and, in particular, in a position such as to remain completely contained in the axial bulk of the brake caliper and facing the opposite way with respect to the ground.
In this way, the bleeding valve is not exposed to possible accidental knocks during use of the bicycle, even though the bleeding valve projects radially in a very pronounced manner from the brake caliper.
The Applicant has found that the maintenance operations carried out by acting on the bleeding valve are not always easy, since the axial distance between it and the wheel of the bicycle is quite small.
The Applicant has realized that a different position of the bleeding valve on the brake caliper, in particular axially distanced from the wheel, would make the maintenance operations carried out on the bleeding valve much easier, such as the venting of air and the insertion of brake liquid in the hydraulic braking system.
The Applicant has however found that such positioning of the bleeding valve could expose it to knocks and damage during normal use of the bicycle, especially in the case in which it projects from the axial bulk of the brake caliper.